Method and apparatus for finishing concrete

ABSTRACT

A power trowel is provided for finishing concrete. The trowel can be used to finish concrete at different stages of hardening. The handle of the trowel is rotated both to adjust the speed of rotation of the trowel blades and to administer a spray solution to the surface of concrete being finished with the trowel. The trowel includes dual rotating hubs with blades attached to and extending outwardly from each hub. The surface areas covered by the blades on one hub overlaps the surface area covered by the blades on the other hub. Each hub rotates in the same direction and non-synchronously with the other hub.

This application is a continuation-in-part of U.S. Ser. No. 12/001,763 filed Dec. 12, 2007 which is a continuation-in-part of U.S. Ser. No. 11/057,019 filed Feb. 11, 2005, which is a continuation-in-part of U.S. Ser. No. 10/315,634 filed Dec. 10, 2002.

This invention relates to a method and apparatus for finishing freshly poured concrete.

More particularly, the invention relates to a concrete finishing method in which a power trowel floats on the liquid-particulate surface of wet concrete to produce a smooth, level surface finish prior to the concrete's hardening.

In another respect, the invention relates to a method for finishing freshly poured concrete in which a power trowel is provided with blades which can be canted during the finishing of concrete so the power trowel can be adapted for finishing concrete at different stages of hardening.

My U.S. Pat. No. 4,740,348 describes a power trowel for finishing concrete. The power trowel is lightweight, and includes a throttle controlled by rotating the handle. While the power trowel set forth in U.S. Pat. No. 4,740,384 is, due to its light weight, especially useful, the power trowel is more difficult to use when concrete becomes stiff as it dries and sets. One way to compensate for the hardening of concrete is to alter the cant of the blades on the power trowel. In conventional trowels, this is accomplished by stopping the trowel and manually adjusting the position of the blades. This procedure is time consuming and can be impractical, especially when the concrete is hardening rapidly.

Accordingly, it would be highly desirable to provide an improved method and apparatus for adapting a light weight power trowel of the type described in U.S. Pat. No. 4,740,348 to permit the ready adjustment of the cant of the blades in order to permit the trowel to be used continuously while freshly poured concrete hardens.

Therefore, it is a principal object of the invention to provide an improved power trowel for finishing freshly poured concrete.

Another object of the invention is to provide a method and apparatus for adjusting the blades of a power trowel simultaneously with operating the power trowel to finish concrete.

These and other, further and more specific objects and advantages of the invention will be apparent from the following detailed description of the invention, taken in conjunction with the drawings, in which:

FIG. 1 is perspective view illustrating a power trowel constructed in accordance with the principles of the invention;

FIG. 2 is a bottom perspective view of the power trowel of FIG. 1 illustrating further construction details thereof;

FIG. 3 is a perspective view of the power trowel of FIG. 1 illustrating further construction details thereof;

FIG. 4 is an exploded perspective view illustrating the hub assembly of the power trowel of FIG. 1;

FIG. 5 is a section view of the hub assembly of FIG. 4 illustrating the mode of operation thereof;

FIG. 6 is a bottom view of the intermediate ball bearing adjustment plate used in the hub assembly of FIGS. 5 and 6 to adjust the cant of the power trowel blades;

FIG. 7 is a top view of the top ball bearing adjustment plate used in the hub assembly of FIGS. 5 and 6, the top ball bearing adjustment plate being identical to the bottom ball bearing adjustment plate;

FIG. 8 is an exploded perspective view of the ratchet assembly used in the power trowel of the invention to adjust the cant of the power trowel blades;

FIG. 9 is a perspective view illustrating the functioning of the handle used on the power trowel of the invention;

FIG. 10 is a top perspective view illustrating a power trowel constructed in accordance with an alternate embodiment of the invention;

FIG. 11 is a top perspective view of one end of the trowel o FIG. 10 illustrating further construction details thereof;

FIG. 12 is a bottom view of the power trowel of FIG. 10; and,

FIG. 13 is a perspective view of a portion of the trowel of FIG. 10 illustrating a belt assembly utilized to rotate the blade units on the trowel.

Briefly, in accordance with my invention, I provide an improved power trowel including a frame including a hub; a rotatable handle having a distal end and having a proximate end attached to the frame; a plurality of spaced apart blades pivotally mounted on and radially extending from the hub, each of the blades having a lower surface area; a transmission assembly mounted on the frame and operatively associated with the blades to pivot and alter the cant of the blades; a cable for activating the transmission assembly to pivot and alter the cant of the blades; a control assembly interconnecting the cable and the handle such that when the handle is rotated, the control assembly displaces the cable to activate the transmission assembly and pivot and alter the cant of the blades; and, an engine mounted on the frame and operatively associated with and rotating the hub.

In another embodiment of the invention, I provide a power trowel including a frame including a hub; a rotatable handle having a distal end and having a proximate end attached to the frame; a plurality of spaced apart blades pivotally mounted on and radially extending from the hub, each of the blades having a lower surface area; a transmission assembly mounted on the frame and operatively associated with the blades to pivot and alter the cant of the blades; a cable for activating the transmission assembly to pivot and alter the cant of the blades; a control assembly interconnecting the cable and the handle such that when the handle is rotated in a first direction, the control assembly displaces the cable to activate the transmission assembly and pivot and alter the cant of the blades; an engine mounted on the frame, having a throttle, and operatively associated with and rotating the shaft; a cable interconnecting the throttle and the handle such that when the handle is rotated in a direction opposite the first direction the cable is displaced and the throttle is adjusted.

In a further embodiment of the invention, I provide an improved method for finishing poured concrete to produce a smooth surface finish on the concrete. The improved method includes the steps of screeding a surface of the poured concrete to preliminarily level the surface of the concrete; moving a bull float over the surface; and, making a pass over the surface with a power trowel. The power trowel includes a frame including a hub; a rotatable handle having a distal end and having a proximate end attached to said frame; a plurality of spaced apart blades pivotally mounted on and radially extending from the hub, each of said blades having a lower surface area; a transmission assembly mounted on the frame and operatively associated with the blades to pivot and alter the cant of the blades; a cable for activating the transmission assembly to pivot and alter the cant of the blades; a control assembly interconnecting the cable and the handle such that when the handle is rotated, the control assembly displaces the cable to activate the transmission assembly and pivot and alter the cant of the blades; and, an engine mounted on the frame and operatively associated with and rotating the hub. The method also includes the step of rotating, while the engine is running and the power trowel is on the concrete, the handle to displace the cable, activate the transmission assembly, and alter the cant of the blades.

In still another embodiment, I provide an improved power trowel including a frame including a hub; a pole having a distal end shaped to be grasped as a handle, a proximate end attached to the frame, a longitudinal axis extending from the distal end to the proximate end, the pole rotatable along its entire length about the longitudinal axis; a plurality of spaced apart blades pivotally mounted on and radially extending from the hub, each of the blades having a lower surface area; a transmission assembly mounted on the frame and operatively associated with the blades to pivot and alter the cant of the blades; a control unit to activate the transmission assembly to pivot and alter the cant of the blades; and, an engine mounted on the frame, having a throttle, and operatively associated with and rotating the hub. The control can comprise a linkage unit interconnecting the transmission assembly and the proximate end of the pole such that when the handle is rotated in a selected direction, the linkage unit is actuated and activates the transmission assembly to pivot and alter the cant of the blades. The transmission assembly can include at least one slotted plate and at least one bearing with an arcuate outer surface and shaped and dimensioned to move along a slot in the plate when the plate is rotatably displaced, the bearing when displaced acting to displace a control member in the transmission assembly to alter the can of said blades. The motor can be a variable speed electric motor.

In still a further embodiment, I provide an improved transmission including at least one slotted plate; and, at least one bearing with an arcuate outer surface and shaped and dimensioned to move along a slot in the plate when the plate is rotatably displaced, the bearing when displaced acting to displace a control member in the transmission.

Turning now to the drawings, which depict the presently preferred embodiments of the invention for the purpose of illustrating the practice thereof and not by way of limitation of the scope of the invention, and in which like reference characters refer to corresponding elements throughout the several views, FIGS. 1 and 2 illustrate a power trowel constructed in accordance with the invention and generally indicated by reference character 10. Trowel 10 includes a frame 9. Engine 11, fuel tank 12, and plate 41 are mounted on frame 9. A drive shaft 140 (FIG. 5) extends from engine 11, through an aperture in frame 9, and to hub 40. When engine 11 is running, it turns shaft 140 and hub 40. Frame 9 can include a safety cage fabricated from tubing made from aluminum or another material. The cage includes concentric circular tubes 31, 32, 33 welded to radial arms 34, 35, 36, 37, 38. Arcuate tube 39 extends from plate 41 to arm 35.

As is illustrated in FIG. 3, tube 39 extends through an arcuate opening 19B (FIG. 3) formed in sleeve 19 and functions as a guide for sleeve 19 along which opening 19B travels when sleeve 19 (and the handle in sleeve 19) is pivoted about pivot point 25 in the direction of arrows 1. Flange 19C at the end of hollow sleeve 19 is pivotally attached by pin 25 intermediate receiving parallel flange pair 24A and 24B.

The proximate end 15 of the handle is rotatably received in sleeve 19. Cylindrical foot 16 extends through opening 19D in sleeve 19 and is fixedly attached to end 15. Rotating the handle in the directions indicated by arrows Y and Z causes foot 16 to rotate side-to-side simultaneously in opening 19D, as indicated by arrows X. One end of linkage assembly or cable 18 slidably passes through upstanding member 17 and is fixedly connected to foot 16. The other end of cable 18 is connected to the throttle (not visible) of motor 11. The handle has an “at rest” or neutral position in which member 17 is centered in elongate aperture 19D. When the distal end 26 of the handle is manually rotated in the direction of arrow Y, member 17 is displaced simultaneously in the direction of arrow Y, pulls on cable 18, and displaces the throttle to increase the flow of fuel to the engine and to increase the RPM of drive shaft 140. When the distal end 26 of the handle is manually rotated in the direction of arrow Z back to the “at rest” or neutral position of the handle, the throttle returns to idle or to a pre-set position in which the drive shaft 140 rotates at a lower RPM. In contrast, when the distal end 26 of the handle is manually rotated from its “at rest” or neutral position in the direction of arrow Z, shaft 210 and foot 200 move in the direction of arrow 211. Shaft 210 interconnects foot 200 and foot 16 and slidably extends through an opening formed in member 17. When the handle is manually rotated from its “at rest” or neutral position in the direction of arrow Y, shaft 210 pulls foot 200 in a direction opposite that of arrow 211. When foot 200 moves in this opposite direction, pawl 201 does not engage or turn toothed gear wheel 204. When, however, foot 200 is moved in the direction of arrow 211 by rotating the handle in the direction of arrow Z from the handle's neutral position, pawl 201 engages and turns wheel 204. Since pulley 207 is connected to toothed wheel 204, pulley 207 turns simultaneously with wheel 204. Pulley 207 rotates in the direction indicated by arrow 212, pulling cable 20 in the direction of arrow 213. When linkage assembly or cable 20 is pulled in the direction of arrow 213, lever arm 22 pivots about pin 180 and the upper end 181 of lever arm 22 (FIG. 2) is displaced in the direction of arrow B. When end 181 is displaced in the direction of arrow B, lower end 182 is displaced in the direction of arrow C. Displacing end 182 in the direction of arrow C pulls hook 184 and tab 21 in the direction of arrow D. As will be described below, pulling tab 21 in the direction of arrow D activates a transmission assembly, causing the blades 50, 60, 70, 80 to rotate to alter the cant of the blades.

Pin 202 is provided on pawl 201 so that when foot 200 is displaced a sufficient distance in the direction of arrow 211, pin 202 rides upwardly on cam surface 205, disengaging pawl 202 from gear wheel 204. This prevents tab 21 from being displaced too far in the direction of arrow D (FIG. 2). Displacing lever arm 214 (FIG. 8) in the direction of arrow 215 functions to release the ratchet assembly such that wheel 204 can free-wheel and the force of gravity acting on the weight of the power trowel will, when the power trowel is setting on the ground, cause blades 50, 60, 70, 80 to rotate back to their original position where blades 50, 60, 70, 80 are more nearly parallel to the ground and are not as severely canted with respect to the ground. Ratchet assembly 19 includes side 209.

As can be seen, the function of the ratchet assembly 19 is, when the handle is rotated, to activate the transmission assembly in the power trowel to cause the cant of blades 50, 60, 70, 80 to be increased. While the ratchet assembly 19 and transmission assembly disclosed herein are presently preferred, any desired ratchet assembly construction and transmission assembly construction can be operatively associated with the rotation of handle and used to accomplish this function. If desired, a mechanism other than a ratchet assembly can be utilized.

In FIGS. 1, 2, and 4 each blade 50, 60, 70, 80 is fixedly attached to an orthogonal block 53, 63, 73, 83, respectively. Each blade is of equal shape and dimension, although this need not be the case. Each block is of equal shape and dimension, although this need not be the case. Each block is fixedly secured to a hollow cylindrical member 52, 62, 72, 82, respectively. Each member 52, 62, 72, 82 is of equal shape and dimension, although this need not be the case. Each member 52, 62, 72, 82 includes an orthogonal opening formed through its center. This orthogonal opening receives the orthogonal end of a control arm. For example, member 62 receives orthogonal end 64 on distal end 68 of arm 65. End 64 and the opening that receives and conforms to end 64 prevent arm 65 from rotating in member 62 and, consequently, cause member 62 and arm 65 to rotate simultaneously.

Each control arm mounted in its associated member 52, 62, 72, 82 is of equal shape and dimension, although this need not be the case. For example, arm 55 has a shape and dimension equal to that of arm 65. Arms 75 and 85 are not visible in the drawings and extend through hollow members 72 and 82 in the same manner that arms 55 and 65 extend through members 52 and 62, respectively.

The proximate end 56, 66, 76 (not visible), 86 of each arm 55, 65, 75, 85 is positioned inside hub 40. Each arm 55, 65, 75, 85 rotatably extends through a hollow cylindrical support member 51, 61, 71, 81, respectively. Each support member 51, 61, 71, 81 is fixedly secured to and outwardly depends from hub 40. A semi-spherical bearing surface 57, 67, 77 (not visible), 87 is fixedly secured to the top of proximate ends 56, 66, 76, 86, respectively. Ends 56, 66, 76, 86 each extend inwardly, and if desired upwardly, from inner cylindrical wall 41 of hub 40 so that when a bearing surface 57, 67, 77, 87 and its associated end 56, 66, 76, 86, respectively, is downwardly pivoted in the direction of arrow V in FIG. 5, arm 55, 65, 75, 85, as the case may be, rotates in the manner indicated by arrows P and Q in FIG. 4. When an arm 55, 65, 75, 85 rotates, the blade 50, 60, 70, 80 mounted on the arm also rotates, increasing the cant of the blade with respect to the surface of concrete being finished. For example, when proximate end 86 and bearing surface 87 are downwardly pivoted through an arc in the direction indicated by arrow R in FIG. 4, member 82 and block 83 rotate or pivot simultaneously with the distal end of arm 85 in the direction indicated by arrow T, and edge 80A pivots upwardly through an arc in the direction indicated by arrow S. When edge 80A pivots upwardly, the cant of blade 80 is increased with respect to the surface of concrete being finished with the power trowel of the invention. Similarly, downwardly depressing arm 66 causes blade 60 to cant such that edge 60A moves upwardly in the direction of arrow H (FIG. 2) and edge 60B moves downwardly in the direction of arrow G. Downwardly depressing arm 56 causes blade 50 to cant such that edge 50A moves downwardly in the direction of arrow E and edge 50B moves upwardly in the direction of arrow F.

The transmission assembly that functions to displace arms 56, 66, 76, 86 is shown in more detail in FIGS. 4 to 7. The transmission assembly includes members 100 and 123; plates 111, 112, 113; circular race 127 with bearings 128 rotatably set therein; circular flat washer 130; and, ball bearings 119 to 122. Upper plate 111 is identical to lower plate 113. Member 100 includes neck 120, upper flat circular surface 103, lower conical surface 104, and externally threaded cylindrical surface 101. Member 123 includes upper conical surface 125 (opposed to conical surface 104 in FIG. 5) and inner cylindrical surface 124. As would be appreciated by those of skill in the art, the transmission assembly can be utilized in machinery other than the concrete finishing apparatus described herein.

As shown in FIG. 6, plate 112 includes tab 21 with aperture 21A formed there through to receive hook 184. Plate 112 also includes arcuate openings 190 to 193 formed at equal intervals in plate 112. Each opening 190 to 193 extends completely through plate 112.

In FIG. 7 plate 111 (and therefore plate 113) includes tab 114 and includes radial grooves 115 to 118 each extending completely through plate 111. Openings 115 to 118 are formed at equal intervals in plate 111. As shown in FIG. 5, tabs 114 of plates 111 and 113 are stacked one on top of the other. In FIG. 2, the stacked tabs 114 are indicated by reference character 26 and extend through opening 114 formed in the frame 9. Since frame 9 is fixed during operation of the power trowel, tabs 114 remain in fixed position in opening 114, preventing plates 111 and 113 from rotating.

When tab 21 is at the “neutral” position shown in FIG. 2, blades 50, 60, 70, 80 are slightly canted from parallel with respect to the surface of the concrete being finished with the power trowel. In this “neutral” position, the blades are typically canted at “preset” angle in the range of two degrees to ten degrees. When tab 21 is in the neutral position, ball bearings 119 to 122 are typically positioned near the outer ends 115A to 118A of the openings 115 to 118 in plate 111 (and plate 113). Plates 111 and 113 are positioned such that each opening in a plate 111 is in registration with an opening in the other plate 113. When tab 21 is in the neutral position, ball bearings 119 to 122 are also typically positioned near the outer ends 190A to 193A of the openings 190 to 193 in plate 112. When ratchet assembly 119 is operated by rotating the handle to displace hook 184—and therefore tab 21—in the direction of arrow D in FIG. 2 and arrow J in FIG. 4, tab 21 is displaced. When tab 21 is displaced, the remaining portion of plate 112 simultaneously rotates in the direction of arrow J. Rotating plate 112 in the direction of arrow J causes the ball bearings to move along openings 190 to 193 toward the inner ends 190B to 193B of said openings. When the ball bearings 119 to 122 move along openings 190 to 193 toward ends 190B to 193B, the bearings also simultaneously roll or slide or move along openings from outer ends 115B to 118B toward inner ends 115B to 118B. When bearings 119 to 122 move toward the inner ends of openings 190 to 192 and of openings 115 to 118, the bearings force sloped surface 125 downwardly away from sloped surface 104 (FIG. 5). When sloped surface 125 (and member 123) are forced downwardly, race 127 and washer 130 are forced downwardly against bearing surfaces 57, 67, 77, 87 to displace downwardly proximate ends 56, 66, 76, 86 in the manner indicated by arrows V (FIG. 5) and R (FIG. 4) to cant blades 50, 60, 70, 80. The concept of utilizing the movement of bearings to force a first surface away from a second surface can be utilized in other machinery or equipment or devices in which such displacement of the second surface can be utilized in the operation of such machinery, equipment, or devices.

In FIG. 5, washer 130 rests on bearing surfaces 57, 67, 77, 87. Apertures 119, 194, and 124, along with similar apertures formed through race 127 and washer 130, permit plates 111 to 113, member 123, race 127, and washer 130 to slide up and down along the outer surface 42 of the hollow internally threaded 43 cylindrical member that depends upwardly from the floor 40A of hub 40. External threads 101 of member 100 turn into internally threaded 43 cylindrical surface. Member 100 is fixedly attached to drive shaft 140 and rotates simultaneously therewith when engine 11 is operating, as does hub 40. Plates 111 to 113 do not rotate with hub 40 and shaft 140. Members 123, 127 and washer 130 may rotate with hub 40, or, rotate at a slower speed due to the friction between bearings 119 to 122 and surface conical surface 125. The outer diameter of race 127 and washer 130 are presently, but not necessarily, equal to the outer diameters of plates 11 to 113.

In use, fresh concrete is poured and is screeded to preliminarily level the surface of the concrete. The concrete is then tamped to bring the fines to the surface. A bull float is moved over the surface of the wet concrete. The bull float ordinarily is fabricated from a material generally free of iron. The power trowel of the invention is then passed over the concrete by starting the engine 11 to rotate the blades and by placing the trowel 10 on the horizontally oriented surface of the concrete. The trowel is moved over the surface of the concrete by grasping the distal end 26 of the elongate generally straight, rigid handle and pulling and pushing the handle to move the trowel over the concrete. The throttle is increased, and the rpm of the blades 50, 60, 70, 80 increased, by manually turning the handle in the direction of arrow Y away from the “at rest” or neutral position of the handle. The cant of blades 50, 60, 70, 80 is increased by turning the handle in the direction of arrow Z to activate ratchet assembly 19 to displace cable 20 and tab 21 to cause the transmission assembly to downwardly displace the proximate ends 56, 66, 76, 86 to cant blades 50, 60, 70, 80 in the manner earlier described. FIG. 9 further illustrates operation of handle 13.

Each linkage assembly or cable 18, 20 can, if desired, be replaced by an alternate linkage assembly comprising a chain, a plurality of interconnected rods, a single rod, a plate, a plurality of interconnected plates, a tube, a plurality of interconnected tubes, a unitary substantially rigid structural member, a unitary elastic structure member, a plurality of interconnected elastic and/or rigid structural members, etc. The structure of the linkage assembly can vary as desired as long as the linkage assembly performs the function of displacing the throttle or lever arm 22, as the case may be, when the handle is manually rotated in the appropriate direction. For example, the linkage assembly can, if desired, include or comprise a motor that is activated when the handle is rotated and that, when activated, functions to displace the throttle or lever arm 22. Or, the linkage assembly can include or comprise a spring or other component that, when the handle is manually rotated, functions to move, or to assist in the movement of, the throttle or lever arm 22.

The handle 200 can consist of a plurality of tube lengths that can telescope, can bolt together, or can otherwise be interconnected. In one preferred embodiment, an end of a cylindrical section of the handle has a reduce diameter that slides into the larger diameter end of a receiving section. The reduced diameter end also is provided with a spring loaded ball bearing that snaps into an opening formed in the larger diameter end of the receiving section when the smaller diameter end slidably seats in the larger diameter end. The ball bearing prevents the smaller diameter end from rotating in the receiving larger diameter end of the receiving section.

FIGS. 10 to 13 illustrate an alternate embodiment of the power trowel of the invention generally indicated by reference character 300. Trowel 300 includes a frame 309. Engine 311 is mounted on frame 309. A drive shaft 340 (FIG. 13) extends from engine 311 and engages continuous belt or chain 341. Belt 341 extends around cylindrical wheel (or a sprocket) 343. Wheel 343 is fixedly mounted on a shaft (not visible) that is fixedly connected to collar 344 (FIG. 13). When engine 11 is running, it turns shaft 340 and moves belt 341 in the directions indicated by arrows A1, A2. When belt 341 is moved in this fashion, it turns wheel 343 and, consequently, collar 344. Wheel 343 is fixedly connected to collar 344. Arms 350 to 353 are connected to and outwardly extend from collar 344. Blades 345 to 348 are mounted on arms 350 to 353, respectively. When collar 344 is rotated by belt 341, blades 345 to 348 and arms 350 to 353 rotate simultaneously with collar 344 in the direction of arrow A3 (FIGS. 12 and 13).

In addition to continuous belt 341, engine 311 and shaft 340 also move a second continuous belt (not visible). The second belt extends from shaft 340 to a wheel (not visible) that is fixedly connected to collar 450 (FIG. 12) and that, when the wheel is turned, turns collar 444 (FIG. 12). Arms 450 to 453 are connected to and outwardly extend from collar 444. Blades 445 to 448 are mounted on arms 450 to 453, respectively. When collar 444 is rotated by the second continuous belt, blades 445 to 448 and arms 450 to 453 rotate simultaneously with collar 444 in the direction of arrow A4 (FIG. 12). Collars 344 and 444, and the blades attached thereto, rotate in the same direction. As would be appreciated by those of skill in the art, trowel 300 can be configured such that shaft 340 supplies motive power to a single belt that turns both collars 344 and 444.

Pole 360 is connected to pole receiver 360A. A pole can also be connected to pole receiver 361A. Poles connected to receivers 360A and 361A can, along with said receivers, be operated in the manner described earlier herein with respect to FIG. 9, or can be configured in any other desired manner. The rotation of collars 344 and 444 in the same direction permits poles 360 to be utilized to steer power trowel 300. The pitch of each blade 345 to 348 and 445 to 448 is preferably, but not necessarily, fixed at a position equivalent to that of the other blades 345 to 348 and 445 to 448. The currently preferred pitch of each blade is five degrees from the horizontal. The distance from the outer tip of a blade 348 to the outer tip of a blade 346 in alignment with blade 348 can vary as desired, but is presently about thirty-four inches.

Trowel 300 is unusually light, presently weighing about forty-six pounds. The lightweight of trowel 300 enable it to begin to surface concrete immediately after the concrete is poured. A long existing dominant trend in the concrete industry is to use heavyweight equipment to finish concrete, including equipment weighing approximately 1000 or more pounds. Concrete must be permitted to cure for about forty minutes to ninety minutes before finishing equipment weighing 1000 pounds can be placed (often by a crane) on the concrete. At that point, the heavy equipment can tend to “tear” and damage the surface of the partially cured concrete. One factor that contributes to the minimal overall weight of trowel 300 is the use of a 25 cc engine 311, preferably an engine with a horsepower rating of less than two, more preferably an engine with a horsepower rate of one or less. An engine with one-half to one horsepower is presently preferred. The rpm of engine 311 is typically in the range of 3000 to 10,000 rpm, preferably 4000 to 9000 rpm. A gear reduction in the range of 75:1 to 140:1 is utilized, preferably in the range of 90:1 to 130:1, so that the output of the engine is reduced to an rpm in the range of fifty to eighty rpm. The engine can include a clutch that engage at 1000 to 3000 rpm.

The outermost tips of blades 345 to 348 rotate along a circular path that overlaps with the circular path along which the outermost tips of blades 445 to 448 rotate. Consequently, if (while blades 346 and 348 remained stationary) blades 445 and 447 were moved in the direction of arrow A4 into alignment with blades 346 and 348 in FIG. 12, the tips of blades 445 and 348 would overlap and contact each other. Such contact is avoided by non-synchronously rotating hubs 344 and 444 at the same number of revolutions per minute such that the outer tip of each blade 345 to 348 arrives at point 500 on housing 350 (FIG. 12) at a different time than does the outer tip of each blade 445 to 448, i.e., at point 500 the outer tip of a blade 345 to 348 is not coincident with the outer tip of a blade 445 to 448. This configuration is illustrated in FIG. 12 where the tip of blade 348 is adjacent point 500 when none of the outer tips of blades 445 to 448 is adjacent point 500. Blade 348 is, in effect, positioned intermediate blade 445 and 446. It follows, therefore, that when the tip of blade 445 is adjacent point 500, blade 445 is, in effect, positioned intermediate blades 347 and 348; when the tip of blade 347 is adjacent point 500, blade 347 is, in effect, positioned intermediate blades 445 and 448; and so on. In this manner, the blades 345 to 348 interdigitate with blades 445 to 448 during operation of power trowel 300.

When collars 344 and 444 rotate in the same direction, forces are generated which act to rotate the entire power trowel 300, including frame 309, in the direction indicated by arrows A5 and A6. A pole receiver 360A is, in one embodiment of the invention, connected to frame 309 such that trowel 300 can rotate in the direction of arrows A5 and A6; and, such that a pole 360 mounted in receiver 360A can be manually rotated to lock receiver 360A to prevent trowel 300 from rotating on receiver 360A in the direction indicated by arrows and A6. Rotating collars 344 and 444 in the same direction also functions to make the trowel 300 stable.

The use of dual pole receivers 360A and 361A facilitates controlling the direction of travel of trowel 300 on concrete that is being surfaced with trowel 300. When a pole 360 is inserted in receiver 360A, the pole is pushed or pulled such that trowel 300 is moved forwardly or rearwardly in the directions indicated by arrows 600 and 601 in FIG. 10. Such movement creates a swath, or path, over concrete that is approximately equal to twice the distance from the outer, or distal, tip of blade 345 (FIG. 11) to the outer tip of blade 347, i.e. is approximately equal to the sum of the swath produced by the rotating blades mounted on collar 344 and of the swath produced by the rotating blades mounted on collar 444. The width of this swath is presently about sixty-four inches, but can vary as desired depending on the distance from the outer tip of one blade 345 to the tip of the opposing blade 347. On the other hand, when a pole 360 is inserted in received 361A, the pole is pushed or pulled such that trowel 300 is moved forwardly or rearwardly in the directions indicated by arrows 602 and 603 in FIG. 10. The width of this swath is currently about thirty-four inches, but can vary as desired depending on the distance from the outer tip of one blade 345 to the tip of the opposing blade 347. Only one pole at a time is utilized, mounted in either receiver 360A or 361A. When a pole mounted in receiver 360A or 361A is lifted upwardly the trowel 300 travels to the right.

Frame 309 include three hollow aluminum tubular concentric oval members 315, 316, 317 (FIG. 10) interconnected by a plurality of radial arms including arms 318 to 323.

Trowel 300 can, in addition to surfacing wet concrete, be used to apply liquid adhesive to floors or to apply other substance that are not overly viscous.

A spray unit 501 (FIG. 10) can be mounted on trowel 300 to dispense water, sealer, or another desired liquid or material on the surface of concrete to facilitate the finishing of the concrete surface. Trowel 300 can be configured such that manually rotating a pole 360 in one direction controls the throttle of engine 311 while rotating the pole in the other direction activates a pump in unit 501 to spray sealer, water, etc. on to the surface of the concrete being finished with trowel 300. 

1. A power trowel including (a) a frame including first and second collars (344, 444); (b) a pole having (i) a distal end shaped to be grasped as a handle, (ii) a proximate end attached to said frame, (iii) a longitudinal axis extending from said distal end to said proximate end, said pole rotatable along its entire length about said longitudinal axis; (c) a plurality of spaced apart blades pivotally mounted on and radially extending from each of said collars, each of said blades having an outer tip and a lower surface area, the area covered by said blades on said first collar overlapping the area covered by said blades on said second collar; (d) an engine mounted on said frame, having a throttle, and operatively associated with and rotating said collars such that said collars (i) each rotate at the same number of rotations per minute, (ii) each rotate in the same direction, (iii) rotate non-synchronously such that one of said outer tips of said blades on said first collar is never coincident with one of said outer tips of said blades on said second collar. 